Applications of same-beam VLBI in the orbit determination of multi-spacecrafts in a lunar sample-return mission

Same-beam VLBI means that two spacecrafts with small separation angles that transmit multi-frequency signals specially designed are observed simultaneously through the main beam of receiving antennas. In same-beam VLBI,the differential phase delay between the two spacecrafts and the two receiving antennas can be obtained within a small error of several picoseconds. As a successful application,the short-arc orbit determination of several hours for Rstar and Vstar,which are two small sub-spacecrafts of SELENE,has been much improved by using the same-beam VLBI data together with the Doppler and range data. The long-arc orbit determination of several days has also been accomplished within an error of about 10 m with the same-beam VLBI data incorporated. These results show the value of the same-beam VLBI for the orbit determination of multi-spacecrafts. This paper introduces the same-beam VLBI and Doppler observations of SELENE and the orbit determination results. In addition,this paper introduces how to use the same-beam VLBI for a lunar sample-return mission,which usually consists of an orbiter,a lander and a return unit. The paper also offers the design for the onboard radio sources in the lunar sample-return mission,and introduces applications of S-band multi-frequency same-beam VLBI in lunar gravity exploration and applications during all stages in the position/orbit determinations such as orbiting,landing,sampling,ascending,and docking.

High-accuracy same-beam VLBI observations using Shanghai and Urumqi telescopes

The same-beam VLBI observations of Rstar and Vstar,which were two small satellites of Japanese lunar mission,SELENE,were successfully performed by using Shanghai and Urumqi 25-m telescopes. When the separation angle between Rstar and Vstar was less than 0.1 deg,the differential phase delay of the X-band signals between Rstar and Vstar on Shanghai-Urumqi baseline was obtained with a very small error of 0.15 mm rms,which was reduced by 1-2 order compared with the former VLBI results. When the separation angle was less than 0.56 deg,the differential phase delay of the S-band signals was also obtained with a very small error of several mm rms. The orbit determination for Rstar and Vstar was performed,and the accuracy was improved to a level of several meters by using VLBI and Doppler data. The high-accuracy same-beam differential VLBI technique is very useful in orbit determination for a spacecraft,and will be used in orbit determination for Mars missions of China Yinghuo-1 and Russia Phobos-grunt.